Conducting polymers by nature are non-soluble and non-dispersible, which makes processing of the polymers difficult and limits their commercial applications. Poor dispersion and difficult processing are the two fundamental obstacles to the development and commercialization of products made using conducting polymers. This invention relates to the synthesis of conducting oligomers and conducting polymers using end-capping monomers. These end-capping monomers, which contain a chemically branched non-conducting group, promote dispersion and processability. Conducting materials made using these branched chemical intermediates are dispersible in some organic solvents. The end-capping monomers can incorporate additional chemical functionality into the conducting material. For example, by incorporating latent polymerizable groups into the end-capping monomers, the conducting material has the added ability to be chemically crosslinked by a polymerization reaction.
Polymers are macromolecules built up by the linking together of larger numbers of much smaller molecules. The small molecules that combine with each other to form polymer molecules are termed monomers, and the reactions by which they combine are termed polymerizations [Principles of Polymerization, 3rd addition, George Odian, John Wiley & Sons, Inc., 1991, pg 1]. Polymers may be made of hundreds to tens of thousands, or more, monomer molecules linked together. In some cases larger molecules are made by combining a small number of monomer molecules together and these compounds are termed oligomers. There is no universally accepted limit to distinguish between molecules termed oligomers and those termed polymers, therefore for the purpose of the present invention oligomers are molecules containing at least 3 and up to 50 monomer molecules and polymers are molecules containing more than 50 monomer molecules.
Intrinsically conducting polymers (ICP) and intrinsically conducting oligomers (ICO) have electrical and optical properties that can be reversibly controlled by changing their oxidation state. Most ICPs and ICOs are conjugated molecules with extended “π” conjugation along the molecular backbone. By chemical or electrochemical oxidation or reduction of the molecular backbone (a process known as “doping”), it is possible to systematically vary the electrical conductivity of these materials from the insulating state to the conducting state. In the doped (conducting) state, ICPs and ICOs consist of rather rigid planar polyionic molecules in which the ionic charges are delocalized over a segment of the molecular backbone. For a p-type conductor “holes” in the valance band of the conjugated material are delocalized, while for an n-type conductor electrons in the conduction band are delocalized. The chains are polycationic when they are doped through oxidation (p-doping) and polyanionic when they are doped through reduction (n-doping). Counter-ions (anions for p-doped polymers and cations for n-doped polymers) are present within the polymeric matrix to compensate for the charges on the polymer. Counter-ions can be organic or inorganic.
Representative ICPs and ICOs include polyacetylene, polyaniline, polypyrrole, polythiophene, poly(phenylenesulfide), poly(para-phenylene), poly(phenylenevinylene), and many others [P. Chandrasekhar, Conducting Polymers, fundamental and Applications, Kluwer Academic Publishers, Boston, 1999]. Because of their extended π conjugation, conducting polymers and oligomer molecules behave like rigid rods, have poor flexibility, and hence do not flow or melt. Therefore, traditional melt processing common in the polymer industry cannot be employed to process these materials. Moreover, because of the strong ionic interactions among polymer chains and counterions, most conducting polymers do not dissolve in either aqueous or organic solvents and, as a result, cannot be processed from solution [Wessling B.; “Dispersion as the key to Processing Conducting Polymers”, in Handbook of Conducting Polymers, 2nd Ed.”, Ed. T. A. Skotheim, R L Elsenbauer, J. R. Reynolds, (1998), Marcel Dekker, New York, p-471-473]. The poor processability of conducting polymers and oligomers is a major impediment to their commercial use.
A few exotic solvents have been discovered for some conducting polymers or oligomers. For example, polyaniline doped with organic sulfonic acids is soluble in m-cresol or hexafluoroisopropanol solutions. However, these solvents are not preferred for large scale industrial processes due to high cost and toxicity [Rasmussen P., Hopkins A., Basheer R., Macromolecules, 29, (1996) 7838-7846]. Other conducting polymers have been stabilized as dilute dispersions in water. For example, a 1.3% aqueous dispersion of poly(3,4-ethylenedioxythiophene), termed PEDOT, doped with polystyrene sulfonic acid is commercially available from H.C. Starck and is sold under the trade name of Baytron™ P (Trademark, Bayer AG and H.C. Starck) (L. Groenendaal, F Jonas, D. Freitag, H. Pielartzik, J. Reynolds, Advanced Materials, 12, (2000) 481-494). However, polystyrene sulfonic acid stabilized dispersions of PEDOT are highly acidic, which can cause problems during product manufacturing. Conducting polymers containing long solubilizing side-chains such as poly(3-hexylthiophene) are soluble in their undoped state in common organic solvents, such as chloroform, and can be processed from solution in this undoped stated. A post processing doping is required to transform the polymer to its conducting form. Post-processing doping is often difficult to carry out, is not homogenous throughout the bulk of the material (the surface of the material has usually a higher doping level) and de-doping in likely to occur with time.
Jong et al. reported the preparation and electronic properties of n- and p-doped phenyl-capped 3,4-ethlenedioxythiophene trimers, which are end-capped conducting oligomers [M Jong, A. Denier van der Gon, X. Crispin, W. Osikowicz, W. Salaneck, and L. Groenendaal, Journal of Chemical Physics, vol 118, no. 14, Apr. 8, 2003, pg 6495-6502]. These materials are being investigated for use in field effect transistors and solar cells. Formula 1 illustrates a phenyl-capped EDOT trimer. The phenyl-capped EDOT trimers were synthesized as model compounds to study the chemical doping of PEDOT. The oligomers were first prepared in the non-doped state, vacuum deposited on substrates, then doped by exposure to iodine or lithium vapor.

Jin et al., reported the preparation of end-capped poly(para-phenylene) oligomers using a trifluorovinyl ether group as the end-cap [J. Jin, S. Glaser, J. Ballato and D. Smith Jr., Polymer Preprints, 2004, vol 45, no (2), page 91]. These fluorinated end-capping groups improved the processability of the poly(para-phenylene) (PPP) conducting material. Non-doped oligomers were made using from 3 to 5 phenylene monomers and were used as non-conducting, luminescent materials. The trifluorovinyl ether end-cap reduced the melting point of the oligophenylenes compared to the non-end-capped parent compound. For example, the melting point of non-doped PPP trimer (oligomer with three phenylene monomers) is 212° C., while it is 168° C. for the fluorinated end-capped trimer. Formula 2 illustrates the structure of the end-capped pentamer reported by Jin, Glaser et al. Poly(para-phenylene) is not a poly(heteroaromatic) compound.

Fujitsuka et al. reported the photoexcitation and electron transfer properties of rod- and coil-type oligo(thienylene-ethynylene)s [M. Fujitsuka, T. Makinoshima, O. Ito, Y. Obara, Y. Aso, and T. Otsubo, Journal of Physical Chemistry B., 2003, Vol 107, pg 739-746]. Oligomers of π-conjugated polymers were synthesized from, among others, 2,5-thienyls, or homo-oligothiophenes. Thiophene monomers were connected with ethynylene groups at the 2 and 5 positions on the thiophene ring. Oligomers with 7 or 11 thiophene rings were produced. Because 2-ethyl thiophene was used as the monomer, the resulting oligomer had one terminal (2-position) end that is end-capped with an ethyl group. The materials produced and reported were not doped, but were used for photoexcitation and electron transfer. Formula 3 is an exemplary oligo(thienylene-ethynylene) end-capped on right.

Rivers et al. reported the synthesis of biodegradable conducting polymers for medical applications [T. Rivers, T. Hudson and C. Schmidt, Advanced Functional Materials, January 2002, vol 12, no. 1, page 33]. As part of the synthesis procedure, an end-capped electroactive oligomer was produced (Formula 4). The electroactive oligomer was made from thiophene and pyrrole, and the end-cap contained a biodegradable ester bond and a terminal hydroxyl group. These oligomer intermediates were reacted with a di-acid chloride to form a biodegradable conducting block copolymer. The oligomer intermediate was not doped during the synthesis procedure.

Cho et al. reported the synthesis and energy transfer characteristics of branched oligo(thienylphenyl)amine compounds [J-S. Cho, Y. Kojima, S, Norifusa, M. Higuchi, K. Yamamoto, Macromol. Chem. Phys. 2003, vol 20, pp 2175-2182]. These molecules have a branched electroactive oligothiophene portion as well as linear hexyl end-caps. The branching only takes place in the oligothiophene region, while the end-caps are linear alkyl groups. None of the compounds described had linear (non-branched) electroactive or conducting segments.
Materials called end-capped conducting oligomers and polymers in the present invention can be classified as triblock copolymers or triblock oligomers, where the ABA triblock structure consists of non-conducting “A” blocks and conducting, or conjugated “B” blocks. Examples of AB diblock copolymers containing a non-conducting “A” block on only one side of the conjugated “B” block are known in the art.
Francois and Olinga reported the preparation of polystyrene-polythiophene (PSt-PTh) copolymers by polymerization of thiophene or 2-bromothiophene and polystyrene precursors terminated with thiophene or 2-bromothiophene groups. Soluble and insoluble fractions were recovered after synthesis. The purified soluble fraction was doped in solution by iron chloride. Doping of the copolymer was quantified by the measuring the optical density of the doping band as a function of the iron chloride loading, but no conductivity data were presented for the copolymer. The copolymer was used to cast films from solution, and these films were then pyrolyzed at 380° C. to de-polymerize the polystyrene. The conductivity of the pyrolyzed films containing only the polythiophene was up to 60 S/cm (B. Francois, T. Olinga, Synthetic Metals, 55-57 (1993) 3489-3494). Francois et al. also described the synthesis of poly(para-phenylene) (PPP), polythiophene (PTh), and poly(3-hexylthiophene) block copolymers with polystyrene (PSt) or polymethylmethacrylate (PMMA) by a similar method. Although they stated that “FeCl3 doped PSt-PPP copolymers” formed “exceptionally regular porous and conducting membranes”, no conductivity data were reported [B. Francois, G. Widawski, M. Rawiso, B Cesar, Synthetic Metals, 69 (1995) 463-466][B. Francois, R Lazzaroni, Ph. Leclere., V. Parente, A. Couturiaux, J. Bredas, Synthetic Metals, 102 (1999) 1279-1282]. These conducting materials produced by the methods described by Francois and Olinga and Francois et al. do not produce end-capped conducting oligomers (where the non-conducting end-caps are on both ends of the oligomer as defined later) or conducting ABA-type block copolymers (where “B” is the conducting polymer segment).
Jin, Liu et al. reported the electrochemical copolymerization of pyrrole and styrene in nitromethane at different feed ratios. The formation of di-block copolymers was reported. The products deposited as insoluble films at the electrode during synthesis, and were insoluble in both nitromethane and dichloromethane. Conductivities ranging from 0.2 to 0.007 S/cm were reported [S. Jin, X. Liu, W. Zhang Y. Lu, G. Xue, Macromolecules, 33, (2000) 4805-4808].
Van Hutten et al. reported the synthesis of block copolymers by regularly alternating a block of oligothiophene with a block of oligosilanylene. The oligothiophene blocks with a specific and definite number of monomer units (thiophene) were first prepared using organometallic chemistry (Ni-catalyzed Grignard coupling of mono- or di-bromothiophenes, or by oxidative coupling of lithiated thiophenes). The oligothiophene blocks, which were not end-capped, were then joined with thiophene terminated silanylene blocks [G. Hadziioannou, P. Hutten, R. Gill, J. Herrema; J. Phys. Chem., 99, (1995) 3218-3224]. Van Hutten et al. report using the silanylene group to limit the conjugation length of conducting polymer segments as a method of controlling the luminescence wavelength. The materials reported were not ABA-type block copolymers.
Leung and Ho Tan reported the synthesis of polystyrene-polyacetylene di-block copolymers produced by thermal elimination of polystyrene-poly(phenylvinylsulfoxide) di-block copolymers. Conductivity of the copolymers versus compositions was reported [L. Leung, K Ho Tan, Macromolecules, 26, (1993) pp. 4426]. Polyacetylene is a conducting polymer but not a poly(heteroaromatic) polymer.
Goodson et al. reported the synthesis of rigid-flexible alternating block copolymers of poly(para-phenylene) and poly(ethylene glycol). The copolymers were characterized by thermogravimetric analysis, differential scanning calorimetry and fluorescence spectroscopy, but no conductivity data were reported [F. Goodson, Z Wagner, T Roenigk, Macromolecules, 34, (2001) 5740-5743]. Goodson et al. report the formation of soluble block copolymers when the PPP segment is less than 6 repeat units long. Although Goodson and others report the formation of block copolymers of PPP that exhibit flourescence behavior, they do not report the formation of conducting materials, or materials that can be rendered conducting by doping. Also, no methods for end-capping conducting oligomers or polymers are reported.
Cao et al. reported the synthesis of ABA block copolymers of polyaniline (“A”) with poly(ethyleneglycol) (“B”) prepared by oxidative co-polymerization of aniline with poly(ethyleneglycol) segments that had previously been reacted with p-aminobenzensulfonyl chloride. The products were reported to be soluble in DMF, DMSO, and THF in the neutral state, but only slightly soluble in the protonated (doped) state. Conductivity of cast films ranged from 0.62 to 1.7×10−4 S/cm [Y. Cao, S. Li, H. Dong, Synthetic Metals, 29, (1989) E329-E336]. The structure of these triblock copolymers is in contrast to the materials of the present invention, in which the “B” block is conducting, or conjugated and the “A” blocks, or end-caps are non-conducting.
Zhang and Bi report the synthesis of polyaniline-poly(phenylene-terephthalamide)-polyaniline tri-block copolymers using an —COCl (acid chloride) end-capped oligomer of poly(phenylene-terephthalamide), and reacting with low molecular weight polyaniline, previously prepared by oxidative polymerization of aniline in HCl solution [G Zhang, X. Bi, Synthetic Metals, 41-43, (1991) 251-254]. In this case the oligo(phenylene-terephtalamide) is end-capped with —COCl groups. The ABA-type block copolymer formed has both conducting “A” and “B” blocks. Also, the “A” blocks are not branched.
Kinlen et al. report the synthesis of ABA tri-block copolymers where the A blocks are polyaniline and the “B” block is a non-conducting di-amino terminated poly(ethyleneoxide), poly(propyleneoxide), poly(dimethylsiloxane), or poly(acrylonitrile-co-butadiene). Polymerization was performed in emulsion by oxidative coupling of aniline and the di-amino terminated “B” block in the presence of dinonylnaphthalene sulfonic acid. Moderately conducting (10−5 S/cm) high molecular weight soluble copolymers were reported [P. Kinlen, B. Frushour, Y. Ding and V. Menon, Synthetic Metals, 101, (1999) 758-761]. These triblock copolymer materials contain a non-conducting “B” block and conducting “A” blocks, which is opposite to the materials of the present invention.
Kinlen et al. (WO99/16084) report the synthesis of diblock AB and triblock ABA copolymers containing intrinsically conducting blocks “A” and a non-conducting block “B.” Diblock copolymers have one non-conducting block and one conducting block, while triblock copolymers have one central “B” non-conducting block and two conducting “A” blocks. Although the published PCT application mentions the use of ICP monomers including “pyrrole, substituted pyrroles, . . . thiophenes and substituted thiophenes, indoles, . . . furans, carbazoles and mixture thereof . . . substituted and unsubstituted anilines . . . ” the only ICP monomer for which copolymer synthesis is reported is aniline and the only block copolymers exemplified are AB di-block and ABA tri-block copolymers of polyaniline (where the polyaniline block is “A”). No methods of preparation are provided in the reference for block copolymers containing blocks of poly(heteroaromatic) polymers such as polypyrrole, polythiophene and their derivatives. This published PCT application does not report methods for forming ABA triblock copolymers where the “B” block is conducting and the “A” blocks are non-conducting, nor does it report the formation of branched conducting copolymers or branched end-capped oligomers.
Luebben et al. report the formation of block copolymers containing at least one block of a poly(heteroaromatic) polymer and at least two blocks of a non-conjugated polymer [S. Luebben, B. Elliott, C. Wilson, United States patent application No. US2003/0088032 A1 (published May 8, 2003) and Published PCT application WO03018648 (published Mar. 6, 2003)]. The ABA-type block copolymers and end-capped oligomers contain “A” blocks or end-caps that are not branched.
McCullough et al. teach a method for forming a triblock copolymer comprising combining a soluble thiophene with an organomagnesium reagent, and in some cases the ends of the polymer contain either an aldehyde, hydroxyl or an atom-transfer-radical-polymerization initiator [McCullough et al. U.S. Pat. No. 6,602,974]. In these cases the end-capping groups on the conducting polymers are linear (not branched) and the 3-alkyl thiophene polymers are not specifically doped. An exemplary hydroxyl terminated 3 alkyl thiophene polymer is given by Formula 5.

In a review of block copolymers (both conducting and non-conducting materials) by Lee et al. the supramolecular structures formed by rod-coil block copolymers are reported [M. Lee, B-K. Cho, and W—C. Zin, Chemical Reviews 2001, vol 101, pp 3869-3892 and references therein.]. Rod-coil block copolymers are discussed including ABA-type block copolymers in which the “B” block is a rigid conducting polymer. All of the materials described are linear block copolymers, and do not contain branched terminal blocks. Lee et al. discuss methods for manipulating the supramolecular structure of conjugated polymers, by incorporating them into coil-rod-coil copolymers, where the conducting segment is the rigid rod. Specific examples are the synthesis of triblock poly(isoprene-block-para-phenyleneethynylene-block-isoprene), and polystyrene-oligothiophene-polystyrene. In both cases the ABA-type block copolymers or the end-caped oligomer intermediates do not contain a branched end-cap or “A” block.
In similar work, Li and Wang reported the synthesis and solution aggregation of polystyrene-oligo(para-phenyleneethynylene)-polystyrene ABA-type triblock copolymers, where “B” is a conducting block [K. Li and Q. Wang, Macromolecules, 2004, vol 37, pp 1172-1174]. The authors state that “aggregation and microphase separation of rod-coil block copolymers containing π-conjugated polymers and oligomers have yielded a number of nanoscale morphologies, such as lamellar, spherical, cylindrical, and vesicular structures with tunable optical and electronic properties”. Furthermore, “compared to the effort directed at understanding the self-assembly of rod-coil di-block copolymers, triblock copolymers containing conjugated moieties are much less studied”. They reported coil-rod-coil triblock copolymers consisting of oligo(-para-phenyleneethynylene) and “found that this triblock copolymer exhibits unique solvatochromatic behavior through aggregation-induced π-πstacking and planarization of the conjugated backbone”. In these experiments the ethynylene units are not heteroaromatic groups and the “coil” or “A” blocks are not branched.
There is a significant and continuing need in the art for conducting polymers and conducting oligomers that exhibit improved processability, optical properties, and physical properties. There is a specific need in the art for processable conducting oligomers and conducting polymers formed from heteroaromatic monomers.